PHOTOELECTRIC AND OPTICAL-PROPERTIES OF GA2SE3 SINGLE-CRYSTALS

Photoelectric properties and optical absorption edge are studied for G a2Se3 single crystals prepared by a special design based on Bridgman t echnique. The dependence of dc and ac photoconductivity on light inten sity; applied voltage and ambient temperature is reported. The forbidd en energy gap at room temperature and the thermal coefficient of energ y gap are calculated and found to be 1.793 eV and -1.31 x 10(-3) eV/de g respectively. The absorption coefficient alpha is measured as a func tion of the photon energy hv of the incident light between 1.901 to 2. 252 eV at various temperatures. Our studies show a peak at a low tempe rature only; this may be due to an exciton state. The optical transiti ons for Ga2Se3 single crystal are found to be allowed direct transitio ns. The optical energy gap is calculated from (alpha(2) - hv) curves i n the temperature range 77-300K. The constants alpha and beta of the V arshni equation are found to be 2.811 x 10(-3) eV K-1 and -615 K respe ctively.